Method of making expanded-metal resistors



Nov. 10, 1925- 1,561,272

H. C. NAGEL METHOD OF MAKING EXPANDED METAL RESISTORS Original FiledMarch '7. 1919 WITNESSES: I INVENTOR His/y GNa eI r v ATTORNEY PatentedNov. 10, 1925.

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Original application fil'ed March 7, I919, Serial No. 281,154@ BatentKc. 1,396382'1, dated. November 192I. Divided and this application filedJune 3,1921. serial No. 474,839.-

To all whom it may concern:

Be it known that I, HARRY C. EAGEL', a citizen of the United States, anda resident of *Wi'lkinsburg, in the county of Allegheny and State ofPennsylvania, have invented: a new and useful Improvement. in Methods ofMaking Expanded-MetalResistors, otwhich the following is aspecification; this application being a -division olt my applicationSerial No. 281,154, filed March 7, 1919, which has matured into PatentNo.1,396,871,.dated November 15,1921.

My invention relates to resistors for elec tric circuits andparticularly to expandedmetal resistors and methodsot making. the

same.

The object of my invention is to provide an improved expanded-metalresistor and a novel method of makingthesame.

In some cases, as where it is desired to control the circuits ofelectric motors on board ship, castegrid. resistors are'unreli ablebecause of their liability to become broken after repeated shocks, and"wire resistors have not the required capacity. Liquid resistors, too,are obviously undesirable. panded metal resistors. have accordingly beentried.

Ordinary expanded metal, however, is unsatisfactory for such usesbecause it cannot be obtained commercially with port-ions unexpanded orin the variety and degree. of expansion to. make: it adaptable forresistor work. A common method of manufacture, which comprises first,slitting the metal sheet and later, pulling the metal apart at theslits, is unsatisfactory because the width of the resulting product isless than that of the original sheet, the walls of some of the slits arepulled apart more than those of others, and, while some of the slitopenings may be larger than is necessary for resistor purposes, thuscausing the resistor to occupy unnecessary additional space, others ofthe openings may be so small as to cause shortcircuits.

Accordingly to the present invention, a strip of uncut metal is operateduptn in such fashion as to simultaneously cut and stretch the metal,whereby the resulting product is of the same width as the origlnal,uncut sheet. The metal is stretched in a direction oblique to the planeof the sheet so as to obtain comparatively large openings between thewalls of the slits without the necessity of taking up. a great deal: ofroom in the plane ofithe grid. "The openings are provided of just. thepro-per size so-that. the maximum amount of resistor material -iscrowded into the" min imum amount of space, without danger of shortcircuits. The open ingsare further of symmetrical form to providefor'the parallel resistance paths'being of equal length. :Ul fi utportions of the metal are left at the ends to serve as terminals. Tolengthenthe electrical, seriespath, the expanded metal is longitudinallyslotted. If a steel or similar alloyis employed, the metal issherardized or otherwise protected against the weather.

- Figurevl. oi the accompanying drawing is a front view of an improvedforms. otmyexpanded metal resistor and Fig. '2 is a side view thereof,looking in the direction of the arrows. i

In forming my expanded-metal resistor, a sheet of metal having therequisite electrical conductivity first out along slits 1 to form alengthened path for the electric current. The sheet is then movedlongitudinally and to one side. The sheet is then cut at slits 2.opposite portions 9" that are not cut at the previous op.erati on. Thesheet is then moved longitudinally in the same direction, Landto theother side, and is cut-at slits'fi opposite the slits first made, and soon" until s much ott'lie sheet has been out as is'desirec l; tionsoftlie metal are" left uncut at the. ends, as shown at t and 5. Uncutportions may also, if desired, be left at the center and at othersecuring places.

Simultaneously with the slitting operation, the metal is stretched in adirection oblique to the plane of the sheet, by reason of the shape ofthe cutting tool, to produce openings 6 which shall be inclined to theplane of the sheet whereby the walls of the openings shall be separatedfrom each other to an appreciable extent, thereby avoidingshort-circuits, but without occupying an unduly large amount of room inthe plane of the sheet. Oblique stretching is obviously better for thispurpose than stretching either in the plane of the sheet or at rightangles thereto. The simultaneous slitting and stretching is effected insuch fashion that the portions of the openings (3 on each side of themetal portions 9 are oi.

the same size and width. The parallel paths of the current are therebyrendered equal in length.

By means of the simultaneous of slitting and stretching, therecontraction in the width ofthe metal, because the stretching operationis effected at a time when the metal that is being stretched iscontiguous to unstretched metal. The resulting product is therefore ofthe same Width as the uneXpan-ded metal and is stiffer than ordinaryexpanded metal.

The metal is then slotted as at 7 to increase the electrical series pathfrom one of the terminals at, longitudinally through the grid to theterminal 5, and then back through the other portion ol the grid to theother terminal 4, and openings 8 are punched, one in the terminalportion 5 and one in each of the terminal portions 4 so as to providefor easily securing the resistor in position in a frame or box by meansof bolts or similar securing means. The metal may then be sherardized orotherwise treated to preserve it from the destructive eli'ects ot theair. Such treatment is particularly sirable if the resistor is to beemployed on board ship.

I have found that, in this manner, a very serviceable grid may beproduced, which entirely satisfactory where cast metal grids and otherresistors are undesirable, which is of uniform quality, having therequisite stiffness, and which is not subject to the defects of ordinaryexpanded-metal resistors.

I claim as my invention:

1. The method of making expanded-metal resistors which comprisesslitting an interior portion of a plane metal sheet between two uncutend portions, simultaneously expanding said slitted portion, thenactuatoperations can be no ing said sheet in the plane thereof and re- 7peuting sald operation, and finally cutting through one of said endportions and said interior portion.

2. The method of making expanded-metal resistors which comprisesslitting a plane metal sheet, simultaneously with the slitting operationstretching the metal obliquely to the plane of said sheet, then soactuating said sheet that upon repetition of said operation, the slitsformed thereby in said sheet are in staggered relation to the slitsformed by said first operation.

3. The method of forming an expandedmetal resistor which comprisessimultaneously cutting and stretching an interior portion of a metalsheet between two uncut end portions, and slitting the resulting productthrough one 01": said end portions and said interior portion.

4. The method of forming an expandedmetal resistor which comprisessimultaneously cutting and stretching an interior portion of a metalsheet between two uncut end portions, slitting the resulting productthrough one of said end portions and said interior portion, punching anopening in each of the slitted end portions and the said other endportion, and treating the resultant product to render it Weatherproof.

5. The method of making an expander metal resistor which comprisesslitting an interior portion of a plane metal sheet between two uncutend portions, simultaneously expanding said slitted portion, thenactuating said sheet longitudinally and to one side and repeating saidoperation, then :10- tuating said sheet longitudinally and toward theopposite side and repeating said operation, and finally cuttingthrougl'i one of said end portions and said interior portion.

In testimony whereof, I have hereunto subscribed my name this 26th davof Mav. 1921.

HARRY C. NAGEL.

